Abstract:The degradation and loss of mountain mires due to global warming or deer impacts have been concerned in Japan, thus records of current vegetation in mountain mires are useful for their future conservation and restoration goals.　Moreover, mire vegetation records in various mountain ranges should enable the evaluation of the environmental factors that affect vegetation in the mires.　However, in Hokkaido, Northern Japan, vegetation has not been surveyed for more than half of the mountain mires, and mire vegetation frameworks considering environmental gradients are very limited.　In this study, we recorded the vegetation of two unsurveyed mires (Kagaminuma Mire and Tekagaminuma Mire) located in the Niseko Mountains, Southwestern Hokkaido in 2020 and 2021.　In addition, we compared vegetation and environmental factors including geography, climate and topography among 23 mountain mires in Hokkaido to reveal the characteristics of the two study mires.　Three plant communities in Kagaminuma Mire and seven plant communities in Tekagaminuma Mire were found.　The major plant communities in these mires dominated by Sphagnum species, Carex middendorffii, and Vaccinium oxycoccos were identified as typical of mountain mires in Central Honshu to Hokkaido.　The cluster analysis of the floristic composition classified the 23 mountain mires into three groups and both two study mires belonged to the group with the lowest number of species and without any alpine species.　Nonmetric multidimensional scaling based on vegetation and correlation analysis with environmental factors indicated that temperature and elevation were the most strongly correlated factors with the ordination (squared correlation coefficient = 0.60-0.89).　The two study mires were characterized by the warmest climate among the mountain mires in Hokkaido.　The close relationship between vegetation and temperature has also suggested that the floristic composition in the mire group with the coldest climate and many unique alpine plants could change because of the future warmer climate.